EP0178404B1 - Metal pipe with protection against corrosion and method for its production - Google Patents

Description

The invention relates to a metallic pipe which is provided with a corrosion protection against chemical and / or mechanical attacks, the corrosion protection consisting of several layers, of which at least a lower layer of metal or a metal alloy forms a metal or metal alloy layer, and an outer plastic layer is provided, and a method for coating.

Such metallic, corrosion-protected pipes serve the purpose of remaining corrosion-resistant even after deformation and during use under impact, impact and bending stress. Such properties are e.g. B. required of motor vehicle parts. It is known (DE-C 2 046 449 / US-A 3 808 057) to provide a galvanized body with a chromate coating and then with a non-wax-like plastic coating, which is then heat-treated. The known method leads to a multilayer protective layer.

It is also known (DE-B 1 246 357) to apply protective coatings to metal objects using aqueous dispersions containing a reducing agent and compounds of hexavalent chromium, using a dispersion in which a hydrophobic resin is not wax-like in character, which may harden or can be thermoplastic, is added.

In contrast, the invention is based on the object of providing a metal object with a multilayer corrosion protection which, with the individual layers being mutually adhesive, is sufficiently flexible for greater deformation and has an even greater resistance to corrosion.

The object is achieved according to the invention in that a metal alloy layer consisting of low-melting metals is applied to the surface of the tube, that an intermediate layer which is adhesive on two sides is applied to the metal alloy layer and that at least one layer of highly resistant thermoplastic material is applied to the intermediate layer or is formed from thermoset. Such a multilayer corrosion protection has high adhesion properties both to the substrate (metal surface) and to one another to the individual layers, and the layers are suitable for higher deformations, such as e.g. B. pipe bends, extremely flexible. Another advantage is the high resistance to tests for base metal corrosion according to DIN 50018 / 2.0 S (tightened industrial atmosphere) or ASTM-B117 (salt spray test). This corrosion protection layer shows a homogeneous behavior when the components are adjusted accordingly.

The effects according to the invention and additional effects can advantageously be achieved in that an intermediate layer which is adhesive on two sides is applied to the metal layer and in that at least one layer of highly resistant, thermoplastic or thermosetting plastic is formed on the intermediate layer.

The effects according to the invention and additional effects can advantageously be achieved in that a chromate layer is applied to the metal or metal alloy layer and in that the chromium layer is coated with the intermediate layer which is adhesive on two sides.

Due to the different melting range and temperature for film formation, the invention can be carried out in such a way that in the case of a metal alloy layer made of low-melting metals, the intermediate layer forms a short-term heat insulation or heat barrier layer and a higher-melting, highly resistant, thermoplastic, plastic or the thermoset is applied as a layer.

A major advantage is that this intermediate layer enables high-melting plastics or thermosets, which require higher temperatures for the reaction, to be applied to low-melting metal alloys. During the application of the plastic, no melts of the metal alloy form, so that accumulations of metal alloy with formation of free zones on the metal object are avoided. The intermediate layer acts temporarily as a barrier layer and prevents the metal alloy from converging in this period. After the plastic has been applied, the intermediate layer creates an extremely intimate connection between the plastic and the metal alloy. These properties have e.g. B. Copolymers, i.e. Synthetic resins of the type in which the adhesion is present even at higher temperatures.

According to a further feature, it is provided as an advantageous metal alloy that the metal alloy layer consists of a lead-tin alloy. Such an alloy is soft and flexible and can also be used economically. The use of a lead-tin alloy also complies with the widespread facilities in this field.

The above alloy is always effective. The best results are achieved if the lead-tin alloy from z. B. 60 parts of lead and composed of 40 parts of tin. This composition is economical and also proves to be safe and permissible for the staff when processing lead. Furthermore, the melting point is relatively low, which saves energy during processing.

When processing such low-melting metal alloys, it is sufficient for the formation of a first corrosion brake that the metal alloy layer has a layer thickness of approximately 4 to 10 11 m. In practice, such a layer thickness is light and the same to be applied moderately and durably in the subsequent deformations of the metal object.

Another alternative is achieved if the metal layer consists of zinc.

It is also advantageous that the metal layer consists of an electrodeposited zinc layer.

According to another development of the invention, it is advantageous that the intermediate layer has a high adhesive force to the metal or metal alloy layer or chromate layer underneath. Such an intermediate layer ensures the desired adhesive strength and at the same time forms a dense, homogeneous surface, which is associated with the desired blocking effect. The intermediate layer is also elastic enough in connection with the metal or the metal alloy to withstand the higher deformations without tearing or even peeling off.

The connection between the metal alloy and the intermediate layer is significantly favored if the temperature for film formation of the intermediate layer is lower than the melting point of the metal alloy layer underneath. At such a temperature ratio, the metal alloy is also prevented from converging.

In the ratio of the intermediate layer to the plastic layer, it is also advantageous that the intermediate layer has a high elasticity and adhesion-promoting properties compared to the plastic layer.

One measure to advantageously increase the corrosion resistance of the metallic tube is to be seen in the fact that further layers of highly resistant plastic are arranged on the intermediate layer.

The layer structure is produced according to the further invention in such a way that the metal or metal alloy layer consists of the melt phase mechanically or galvanically in a continuous process, the intermediate layer consists of a primer, in the flood process or by spraying on from a solvent phase or dispersion phase or electrostatically from the solid phase and the plastic in the flooding process, by spraying from a solvent phase, a dispersion phase or electrostatically from the solid phase.

The operational requirements correspond to the fact that the metal alloy layer is applied at a temperature of approx. 190 to 235 ° C.

Accordingly, an economically working process is based on the fact that the highly resistant plastic is baked, dried or melted at a temperature of approximately 240 to 270 ° C.

The metallic tube, in particular made of steel, is particularly recommended for use as brake lines, fuel and hydraulic lines for motor vehicles.

• Fig. 1 einen Querschnitt eines Rohres mit einfacher Kunststoffbeschichtung,
• Fig. 2 einen Querschnitt eines Rohres mit doppelter Kunststoffbeschichtung,
• Fig. 3 einen Querschnitt eines Rohres mit einer Chromatschicht und einfacher Kunststoffbeschichtung,
• Fig.4 4 einen Querschnitt eines Rohres mit einer Chromatschicht und doppelter Kunststoffbeschichtung.

Exemplary embodiments of the invention are shown schematically in the drawing and are explained in more detail below. Show it:

• 1 shows a cross section of a tube with a simple plastic coating,
• 2 shows a cross section of a tube with a double plastic coating,
• 3 shows a cross section of a tube with a chromate layer and a simple plastic coating,
• Fig.4 4 shows a cross section of a tube with a chromate layer and double plastic coating.

In the exemplary embodiment, the tube 1 forms a seamless, welded or double-walled rolled tube. Corrosion protection against chemical and / or mechanical attacks, which consists of several layers, is applied to this tube 1. On the pipe surface 2 of the pipe 1 itself, a metal alloy layer 3 is first applied in the usual process, the composition of which, for. B. provides two low-melting metals. In the exemplary embodiment, lead and tin are used in an alloy ratio of 60:40. After this metal alloy layer 3 has solidified, an intermediate layer 5, e.g. B. applied a primer. The intermediate layer 5 consists of a binder system which is a synthetic resin and among other things. contains corrosion-inhibiting fillers. The intermediate layer 5 initially acts as an adhesion promoter and is therefore extremely adhesive to the side of the metal alloy layer 3. On the other hand, the intermediate layer 5 adheres to a high-resistance, thermoplastic plastic layer 6 which is then to be applied, and thermosets can also replace it, as described. Polyvinyl fluoride (PVF) or polyvinyl difluoride (PVF2) are particularly suitable.

The layer thickness of the metal alloy layer 3 is approximately 4 to 10 J.1.m, so that production can be carried out in a high-speed process. The intermediate layer 5, i.e. the so-called primer is chosen as the synthetic resin so that there is a high adhesive force to the underlying metal alloy layer 3.

In a special embodiment, the intermediate layer 5, like the plastic layer 6, has a high elasticity, adhesion-promoting properties and temperature stability.

According to FIG. 2, a further layer 6 made of highly resistant plastic or highly resistant duroplastic is provided. The application of a further layer 6 does not require an additional intermediate layer.

The evaluation of pipe 1, which is protected against corrosion according to the invention, becomes clear when the following tests are carried out:

A steel tube 1 which was only tin-plated would not withstand the test according to ASTM-B117 (salt spray test), ie such a tube would show base metal corrosion (red rust) after approx. 360 hours. The test according to DIN 50018 / 2.0 S (tightened industrial atmosphere) would only be lead tinned tube also give poor test results. According to DIN 50018 / 2.0 S (corresponds to 2 liters of S02), only one lap to visible base metal corrosion is achieved.

A galvanized steel tube, which is provided with a chromate layer as well as with a plastic layer, reaches over 50 rounds according to DIN 50018 / 2.0 S or over 5000 hours according to ASTM-B 117 until base metal corrosion.

According to the invention, a resistance of over 50 rounds in accordance with DIN 50018 / 2.0 S or 5000 hours in accordance with ASTM-B 117 is likewise achieved in steel pipes with the layer structure of lead-tin, intermediate layer and plastic layer Layer structure zinc, intermediate layer and plastic layer a resistance of over 60 rounds according to DIN 50018 / 2.0 S or 7500 hours according to ASTM-B 117. You can also (according to Fig. 3 or 4) between metal layer or metal alloy 3 and the intermediate layer 5 Apply a chromate layer 4, the resistance to avoid infiltration, such as z. B. in the event of injury (e.g. rockfall), positively influenced.

Claims (17)

1. Metallic tube which is provided with a corrosion protection against chemical and/or mechanical attacks, the corrosion protection consisting of a plurality of layers of which at least one under layer of a metal or a metal alloy forms a metal alloy layer (3), and an outer synthetic plastics material layer (6) is provided, characterised in that on the surface (2) of the tube a metal alloy layer (3) consisting of low-melting metals is applied, in that on the metal alloy layer (3) there is applied an intermediate layer (5) capable of adhesion on both sides and in that on the intermediate layer (5) there is formed at least one layer (6) of high-resistance, thermoplastic synthetic plastics material or of thermosetting synthetic plastics material.

2. Metallic tube which is provided with a corrosion protection against chemical and/or mechanical attacks, the corrosion protection consisting of a plurality of layers of which at least one under layer (3) is formed from a metal, and an outer synthetic plastics material layer (6) is provided, characterised in that an intermediate layer (5) capable of adhesion on both sides is applied on the metal layer (3) and in that on the intermediate layer (5) there is formed at least one layer (6) of high-resistance thermoplastic synthetic plastics material or thermosetting synthetic plastics material.

3. Metallic tube according to Claim 1 or 2, characterised in that a chromate layer (4) is applied on the metal or metal alloy layer (3) and in that the intermediate layer (5) capable of adhesion to both sides is applied on this chromate layer (4).

4. Metallic tube according to Claim 1, characterised in that in the case of a metal alloy layer (3) of lowmelting metals the intermediate layer (5) forms a brief thermal insulation or heat blocking layer and a higher melting high-resistance thermoplastic synthetic plastics material or thermosetting plastics material are applied as layer (6).

5. Metallic tube according to Claims 1, 3 and 4, characterised in that the metal alloy layer (3) consists of a lead-tin alloy.

6. Metallic tube according to Claims 1, 3, 4 and 5, characterised in that the lead-tin alloy is composed for example of 60 parts lead and 40 parts tin.

7. Metallic tube according to Claims 1, 3 to 6, characterised in that the metal alloy layer (3) has a layer thickness of approximately 4 to 10µm.

8. Metallic tube according to Claim 2, characterised in that the metal layer (3) consists of zinc.

9. Metallic tube according to Claims 2 and 8, characterised in that the metal layer (3) consists of a galvanically deposited zinc layer.

10. Metallic tube according to Claims 1 to 6, characterised in that the intermediate layer (5) has a high adhesion power to the metal or metal alloy layer (3) or chromate layer (4) situated therebeneath.

11. Metallic tube according to Claims 1 to 10, characterised in that the temperature for film formation of the intermediate layer (5) lies lower than the melting point of the metal alloy layer (3) situated therebeneath.

12. Metallic tube according to claims 1 to 11, characterised in that the intermediate layer (5) possesses a high elasticity and adhesion-communicating property.

13. Metallic tube according to Claims 1 to 12, characterised in that further layers (6) of high-resistance synthetic plastics material are arranged on the intermediate layer (5).

14. Process for coating the metallic tube according to Claims 1 to 13, characterised in that the metal or metal alloy layer (3) is applied out of the molten phase mechanically or galvanically by the continuous-flow method, the intermediate layer (5), consisting of a primer, is applied by the flood method or by spray application out of a solvent phase or dispersion phase or electrostatically out of the solid phase, and the synthetic plastics material (6) is applied in the flood method, by spray application out of a solvent phase or dispersion phase or electrostatically out of the solid phase.

15. Process according to Claim 14, characterised in that the metal alloy layer (3) is applied at a temperature of about 190 to 235°C.

16. Process according to Claim 14, characterised in that the high-resistance synthetic plastics material (6) is fired, dried and/or fused at a temperature of app. 240 to 270° C.

17. Metallic tube, especially of steel, according to Claims 1 to 13, characterised in that it serves as brake conduits, fuel and hydraulic conduits for motor vehicles.

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